Devices of this kind, particularly kitchen utensils used for making pasta, include a cylinder which usually is centered on a more or less vertical axis and contains a piston rod designed to expel the contained dough through an extrusion nozzle disposed at one end--generally the lower one--of that cylinder. A piston rod projects from the opposite cylinder end and is intermittently displaceable, with the aid of an operating lever articulated to the cylinder near that end, toward the nozzle end thereof. The lever, which is limitedly swingable in an axial plane of the cylinder, coacts with the rod through a one-way coupling so as to advance same on a forward swing (e.g. downward) and to release that rod on a reverse swing whereby the dough is progressively converted into the type of shaped products known as pasta. The one-way coupling may comprise a thrust member in the form of a pawl pivoted on or resiliently connected with the lever for drivingly engaging a sawtooth-shaped serration on a longitudinal surface of the piston rod; see, for example, German Pat. Nos. 958,011 and 2,704,432 (the latter being owned by the assignee of my present application). The first of these German patents also teaches the provision of a second serration on an opposite longitudinal surface of the piston rod, these two serrations being of different pitch and being alternatively juxtaposable with the driving pawl in order to let the user select a larger or a smaller advance of the piston on a given forward swing of the lever. Turning the rod through 90.degree. confronts that pawl with a smooth surface so as to enable the unhindered manual retraction of the piston.
Another type of one-way coupling, described in German printed specification No. 11 40 525 published Dec. 6, 1962, discloses a one-way coupling in the form of an apertured plate which, upon an upswing of the operating lever against a fixed stop acting as a fulcrum, is tiltable into an inclined position in which the smooth piston rod is gripped between opposite edges of the plate aperture so as to execute a downward step. A similarly tiltable spring-loaded plate serves as a backstop. The frictional clamping of the rod by this kind of coupling enables only limited pressure to be exerted upon the piston head unless the applied force is so large that, with the apertured plate harder than the rod, the latter is notched by the gripping action.
Even with the positively acting pawl-type coupling described above, the known constructions require operating levers of considerable length in order to afford a suitable mechanical advantage in advancing the piston. This is due to the fact that, with the pivotal axis of the lever located at the far side of the piston rod as seen from the free lever end, the load arm measured between that pivotal axis and the junction of the driving pawl with the lever is relatively large and, as shown in German Pat. No. 958,011, may be about equal to the cylinder radius. The operating lever and other parts of the mechanism must therefore be able to sustain and transmit the considerable force which the user is required to apply. In the past, therefore, the devices here considered were generally made of metal.